Copy protection system for optical discs

ABSTRACT

A system for copy protection of record carriers for digital data is described according to which at least one predetermined repetitive bit pattern which encodes into channel bits having an accumulated digital sum value that exceeds a first predetermined limit and that is below a second predetermined limit is determined and recorded onto said record carrier by a mastering process so that said accumulated digital sum value which exceeds said first predetermined limit and is below said second predetermined limit is achieved in said at least one replaced and/or inserted part.

The present invention relates to a copy protection method for recordcarriers, i.e. storage media, which store digital data as anasynchronous signal, e.g. Compact Discs (CDs) and Digital VersatileDiscs (DVDs) including all existing or future formats of CD and DVD orother Optical Storage Media which work according to a similar concept.

In particular, the copy protection method according to the presentinvention allows to make a physical copy or creating a complete dataimage of the media content, but the physical copy itself is notaccessible anymore or the access is disturbed or that the error rate isincreased dramatically so that e.g. listening to the music content of acopied audio CD is not entertaining anymore.

Optical storage discs with information stored on one or both sides havecome to be used for a variety of purposes, most notably in the music,games, video and computer industry. Digital information is stored on theoptical storage media in the form of pits arranged along circular,concentric tracks on one or on both sides of the disc. The track istypically read from the inside out, but may also be read form outsidein, as it is already used for some optical storage media.

The data itself on the track is subdivided into frames, each equal inlength, containing equal amounts of information. Each frame has adedicated layout depending on the type of optical storage media (CD,DVD). Such a frame always contains the user data symbols itself but mayalso contain data for synchronization, merging data between data symbolsand error correction.

The signal on a optical storage medium itself is asynchronous, whichmeans that in the decoding process synchronization, timing information,parity data or other data has to be spied out from the signal.

Due to the nature of such storage media copies can be made easily. Tocope with this situation, there exist various copy protection schemeswhich try to prevent unauthorized access with the help of keys orpasswords stored on the respective storage medium itself. Further, thereexist methods which secure an optical disc with the help of storedinvalid information which gets repaired during the copy process so thatan application program can determine whether it is stored on an originalor on a copy based on the presence or absence of this invalidinformation.

Further, U.S. Pat. No. 6,005,839 describes a copy protection scheme foroptical record carriers, in particular DVDs, according to which director dump copying is prohibited by inserting a synchronization pattern atan irregular position different from the regular position or byinserting a synchronization pattern different to the standardsynchronization pattern at the regular position of certain areas orsectors of the optical record carrier. To assure an undisturbedreproduction of such a record carrier the reproducing obstructing areacreated with the misleading synchronization patterns is skipped byjumping based on position designating information (designating thereproducing obstructing area) which is recorded on the record carrier,preferably in the Table Of Contents (TOC) area.

Further, according to WO 01/78074 which content is herewith incorporatedinto this specification, additionally generated data which confuses areading device gets written to at least one specific portion of therecord carrier, e.g. the beginning of a sequence, so that a generalpurpose reading device which can access record carriers of differentformats, e.g. a CD-ROM, which accesses said record carrier judges saidrecord carrier to be inaccessible, i.e. that a record carrier accordingto that teaching comprises at least one specific portion with suchadditionally generated data.

Therewith, according to that teaching such additionally generated datawhich confuses a reading device is inserted in such areas which are notaccessed by a reading device designed for that type of record carriers,e.g. a normal audio CD player for audio CDs, but which are alwaysaccessed by a general purpose reading device, e.g. a CD-ROM readingdevice, so that these reading devices will abort the reading or accessof the record carrier.

However, due to the fact that such record carriers are generally notaccessible by e.g. CD-ROM reading devices, users who want to also usethese record carriers on their computers are not satisfied.

U.S. Pat. No. 5,699,434 which content is herewith included by referenceinto this specification discloses a method of inhibiting copying ofdigital data according to which a sequence of symbols is added to theoriginal data, wherein the sequence of symbols is selected to encodeinto channel bits having a large accumulated digital sum variance (DSV).The sequence of symbols is then encoded by a special encoder thatgenerates special channel bits that do not have a large accumulateddigital sum variance so that no playback problems will occur. However,in case of a normal encoding of the accessed data including the addedsequence of symbols for the purpose of copying or further recording,i.e. a re-encoding, channel bits having a large accumulated digital sumvariance will be likely generated. The generated digital sum values canbe used to encode additional data, e.g. by their sign, so that otherencoders will encode the same original data into channel bits that donot include this additional data which might be used for decrypting,descrambling or otherwise modifying the original data. Further, it isstated that other encoders might also encode the same original data inchannel bits that cannot be recovered.

However, according to this copy protection method always a specialencoder is necessary adapted to encode the selected sequence of symbolswhich would normally encode into channel bits having an accumulateddigital sum variance that exceeds a predetermined limit non-optimallyinto channel bits having an accumulated digital sum variance that doesnot exceed the predetermined limit. Due to the needed special designsuch an encoding can become costly.

Therefore, it is the object underlying the present invention to providea further copy protection system for record carriers which store digitaldata as an asynchronous signal.

The method to produce a copy protected record carrier for digital dataaccording to the present invention is defined in independent claim 1.Preferred embodiments thereof are defined in the dependent claims 2 to11. A device to produce a record carrier with copy protection accordingto the present invention is defined in independent claim 13 and a copyprotective record carrier according to the present invention is definedin independent claim 14. A computer program product according to thepresent invention is defined in claim 12.

Independent claims 15 and 16 define methods to copy digital data storedon a record carrier with copy protection according to the presentinvention onto a recordable record carrier, i.e. an evasion of the copyprotection system according to the present invention. A correspondingcomputer program product is defined in claim 17 and claim 18 defines acomputer storage means storing thereon such a computer program product.Claims 19 and 20 define corresponding devices to copy digital datastored on a record carrier with copy protection according to the presentinvention onto a recordable record carrier.

The method to produce a copy protected record carrier for digital dataaccording to the present invention comprises the steps of:

-   -   determining at least one predetermined repetitive bit pattern        which encodes into channel bits having an accumulated digital        sum value that exceeds a first predetermined limit and that is        below a second predetermined limit,    -   replacing at least one part of the digital data to be recorded        by the at least one predetermined repetitive bit pattern and/or        inserting the at least one predetermined repetitive bit pattern        into at least one part of the digital data to be recorded, and    -   transferring said digital data including the at least one        replaced and/or inserted part onto said record carrier by a        mastering process so that said accumulated digital sum value        which exceeds said first predetermined limit and is below said        second predetermined limit is achieved in said at least one        replaced and/or inserted part.

Therewith, according to the present invention at least one predeterminedbit pattern is included on at least one part of an optical recordcarrier, which effects therein a generation of a predetermined ratioabove the average ratio of successively following pits or lands due tothe exceeding of the digital sum value or running digital sum (RDS)above a first predetermined limit, since in a ideal case the digital sumvalue is equal to zero. On the other hand, due to the definition of thesecond predetermined limit, accessibility of the record carrier producedaccording to the present invention is secured, although tolerable orcorrectable errors might be included. The first predetermined limitshould be chosen so that the accumulated effects of the digital sumvalue exceeding said first predetermined limit and a boosting of thetracking servo disturbance resulting therefrom when a copy of thepredetermined bit pattern is recorded onto a recordable record carrierassures that the copy is not accessible or the access is disturbed sothat e.g. listening to the music content of a copied audio CD is notentertaining anymore. This boosting might be an effect of aninterference between the signal of the wobbled groove of a recordableoptical record carrier and the track following signal coming of theregular pit/land pattern resulting from the regular bit pattern.

In case of an audio CD the predetermined bit pattern is preferablyincluded, i.e. inserted or replacing other digital data, so that:

-   -   different predetermined bit patterns might be used for different        audio channels,    -   at least one part of the digital data to be replaced might        correspond to silence of digital audio data,    -   at least one part of the digital data to be replaced might be        arranged in a portion of the record carrier which is the target        position for a (possible) jump of the reading beam,    -   at least one part of the digital data to be replaced might be        arranged in an introductory portion of a track (song) of digital        audio data, and/or    -   at least one part of the digital data to be replaced might be        arranged in an end portion of a track (song) of digital audio        data.

The predetermined bit pattern is repetitive, i.e. a predetermined numberof bits is repeated a predetermined amount of times so that the replacedor inserted part preferably fulfils the following requirements:

-   -   long enough to properly disturb access or lead to abortion of        access,    -   in case of audio a non or hardly hearable signal is generated,        further preferably bit patterns corresponding to ramp signals        are also included within the replaced or inserted part before        and after the repetitive bit pattern so that a smooth transition        to and from the signal corresponding to the inserted part is        ensured, and/or    -   the order of the repetitive bit pattern results into a regular        bit pattern after interleaving according to the CIRC encoder        described in the Red Book or IEC-908, respectively.

In case of a CD-ROM the predetermined bit pattern is preferablyincluded, i.e. inserted or replacing other digital data, so that:

-   -   at least one part of the digital data to be replaced might        correspond to those areas which are filled by 0-data, normally,    -   at least one part of the digital data to be replaced might be        arranged in a position of the record carrier which is the target        position for a (possible) jump of the reading beam,    -   at least one part of the digital data to be replaced or inserted        might be arranged in a portion of the record carrier which is        not accessed by the reading beam during normal access of the        record carrier,    -   at least one part of the digital data to be replaced or inserted        might be arranged at the end of a data file or directory record        as dummy data.

In the method according to the present invention, said predeterminedrepetitive bit pattern is preferably selected so that an abnormalwriting beam deviation from the ideal position of a writing beam of arecord carrier recording device for recordable record carriers whichwriting beam deviation is big enough to ensure that a writing processwill be aborted or disturbed.

Alternatively or additionally, in the method according to the presentinvention, said predetermined repetitive bit pattern is preferablyselected so that an abnormal reading beam deviation from the idealposition of a reading beam of a record carrier reading device whichreads a copy of the copy protected record carrier recorded on arecordable record carrier which reading beam deviation is big enough toensure that a reading process will be aborted or disturbed.

Further alternatively or additionally, in the method according to thepresent invention, said predetermined repetitive bit pattern ispreferably selected so that an abnormal writing beam deviation from theideal position of a writing beam of a record carrier recording devicefor recordable record carriers and is selected so that an abnormalreading beam deviation from the ideal position of a reading beam of arecord carrier reading device which reads a copy of the copy protectedrecord carrier recorded on a recordable record carrier wherein thecombined effect of writing beam deviation and reading beam deviation isbig enough to ensure that a reading process will be aborted ordisturbed.

Still further alternatively or additionally, in the method according tothe present invention, said predetermined repetitive bit pattern ispreferably selected so that an abnormal reading beam deviation from theideal position of the reading beam of a record carrier reading devicewhich reads the copy protected record carrier which deviation is smallenough to ensure a readability of the copy protected record carrier. Asmentioned above, readability is to be understood in the sense thatreading errors are tolerable or correctable.

Still further alternatively or additionally, in the method according tothe present invention, said predetermined repetitive bit pattern ispreferably selected so that merge bits are predefined and therefore notchangeable by the recording electronic of a recorder due to design rulesof the digital data content of the record carrier. This case includesthat the merge bits might be selected from the recording electronic ofthe recorder from a group of predefined merge bits which all fulfil therequirements according to the present invention, i.e. which all lead tothe desired effect, even if the recording electronic selects those mergebits which result in the lowest possible digital sum value. Such a groupof predefined merge bits might be 100, 010, 001 which all have the sameeffect that the status of the following bits gets inverted, but theposition of the inversion is changed. Due to this “variable” positionalso the digital sum value is variable within certain limits. In generalthe recording electronic of the recorder will select those merge bitswhich will lead to the lowest digital sum value, which, however, can bechosen on basis of the predetermined repetitive bit pattern to fulfilthe requirements according to the present invention.

Still further alternatively or additionally, in the method according tothe present invention, said predetermined repetitive bit pattern ispreferably selected so that the signal corresponding to the digital datashows a certain positive or negative digital sum value within apredefined time.

Still further alternatively or additionally, in the method according tothe present invention, in case of audio, said predetermined repetitivebit pattern is preferably selected so that a low analog audio DC valueis achieved.

Still further alternatively or additionally, in the method according tothe present invention, in case of audio, said predetermined repetitivebit pattern is preferably selected so that an equal analog audio DCvalue in all audio channels is achieved.

Still further alternatively or additionally, in the method according tothe present invention, in case of audio, said predetermined repetitivebit pattern is preferably selected so that an audio output signalcorresponding to the digital data is achieved, which analog audio outputsignal has a frequency and/or amplitude which cannot be heard or canhardly be heard by humans.

Still further alternatively or additionally, in the method according tothe present invention, in case of audio, preferably before and aftersaid predetermined repetitive bit pattern a ramp signal is added whichensures a smooth transition from and to the digital data signal contentbefore and after the signal content of the predetermined repetitive bitpattern.

A corresponding computer program product according to the presentinvention comprises computer program means adapted to perform the methodsteps as defined above or parts thereof when being executed on acomputer, digital signal processor, or the like. In particular, parts ofthe method steps is to be understood in the sense that the determiningat least one predetermined repetitive bit pattern needs not to beperformed by the computer program product according to the presentinvention, i.e. that the predetermined repetitive bit pattern might bedetermined outside the computer program product, e.g. by way of trialand error. Of course, respective predetermined bit patterns might alsobe determined by the computer program product according to the presentinvention according to design rules as set out above.

A device to produce a record carrier with copy protection according tothe present invention comprises

-   -   a first unit for replacing at least one part of the digital data        to be recorded by at least one predetermined repetitive bit        pattern and/or for inserting at least one predetermined        repetitive bit pattern into at least one part of the digital        data to be recorded, wherein said repetitive bit pattern encodes        into channel bits having an accumulated digital sum value that        exceeds a first predetermined limit and that is below a second        predetermined limit, and    -   a second unit for transferring said digital data including the        at least one replaced and/or inserted part to a record carrier        production unit which produces said record carrier by a        mastering process so that said accumulated digital sum value        that exceeds a first predetermined limit and is below a second        predetermined limit is achieved in said at least one replaced        and/or inserted part.

The predetermined repetitive bit pattern might be generated and/orcomprise the characteristics as described above in connection with themethod according to the invention.

A copy protected record carrier according to the present inventioncomprises at least one part comprising at least one predeterminedrepetitive bit pattern which encodes into channel bits having anaccumulated digital sum value that exceeds a first predetermined limitand is below a second predetermined limit.

The predetermined repetitive bit pattern might be generated and/orcomprise the characteristics as described above in connection with themethod according to the invention. The record carrier according to thepresent invention is preferably an optical record carrier, e.g. a CD orDVD.

The copy protection system according to the present invention could beovercome by a removal, replacement or reencoding of the predeterminedrepetitive bit pattern(s) according to the present invention which areincluded on a record carrier according to the present invention. Toachieve this, the predetermined repetitive bit patterns according to thepresent invention have to be searched and processed.

Therefore, a method to copy digital data stored on a record carrier withcopy protection onto a recordable record carrier according to thepresent invention comprises the following steps:

-   -   searching for at least one part of digital data to be copied        onto said recordable record carrier comprising at least one        predetermined repetitive bit pattern which would encode into        channel bits having an accumulated digital sum value that        exceeds a first predetermined limit and is below a second        predetermined limit, and    -   replacing said at least one part by a bit pattern which encodes        into channel bits having an accumulated digital sum value that        is below said first predetermined limit, or for deleting said at        least one part.

Alternatively, a method to copy digital data stored on a record carrierwith copy protection onto a recordable record carrier according to thepresent invention comprises the following steps:

-   -   searching for at least one part of digital data to be copied        onto said recordable record carrier comprising at least one        predetermined repetitive bit pattern which would optimally        encode into channel bits having an accumulated digital sum value        that exceeds a first predetermined limit and is below a second        predetermined limit, and    -   encoding said at least one part non optimal into channel bits        having an accumulated digital sum value that is below said first        predetermined limit.

A corresponding computer program product according to the presentinvention, comprising computer program means adapted to perform themethod steps as defined in the both paragraphs above when being executedon a computer, digital signal processor, or the like.

A computer storage means according to the present invention comprises acomputer program product according to the above paragraph.

Further, a device to copy digital data stored on a record carrier withcopy protection onto a recordable record carrier according to thepresent invention comprises

-   -   a searching unit to search for at least one part of digital data        to be copied onto said recordable record carrier comprising at        least one predetermined repetitive bit pattern which would        encode into channel bits having an accumulated digital sum value        that exceeds a first predetermined limit and is below a second        predetermined limit, and    -   a replacement unit for replacing said at least one part by a bit        pattern which encodes into channel bits having an accumulated        digital sum value that is below said first predetermined limit,        or for deleting said at least one part.

Alternatively, a device to copy digital data stored on a record carrierwith copy protection onto a recordable record carrier according to thepresent invention comprises

-   -   a searching unit to search for at least one part of digital data        to be copied onto said recordable record carrier comprising at        least one predetermined repetitive bit pattern which would        optimally encode into channel bits having an accumulated digital        sum value that exceeds a first predetermined limit and is below        a second predetermined limit, and        an encoding unit for encoding said at least one part non optimal        into channel bits having an accumulated digital sum value that        is below said first predetermined limit.

In this specification the term channel bits is used for the bit patternthat satisfies the various constraints for digital data as anasynchronous signal, such as a trade-off between recording density anderror rate, the highest permissible transition frequency, self-clocking,the NonReturn to Zero Inverted (NRZI) format which has a run lengthlimited (RLL) code, e.g. for compact discs usually the (2,10)-RLL, whichmeans that the number of consecutive zeros in the encoded bit patternmust be at least 2 and no greater than 10, an requirement for a limit onthe low frequency content of the read signal, and so on.

According to the present invention advantage is taken from the effectthat reading devices do not fail to correctly read record carriers whichcomprise bit patterns which show an accumulated digital sum value thatexceeds a first predetermined limit and that has to be below a secondpredetermined limit. When now determining the first predetermined limitso that upon recording this bit pattern onto a recordable record carrierautomatically the above described boosting of the tracking servodisturbance assures that the copy is not accessible or the access isdisturbed so that e.g. listening to the music content of a copied audioCD is not entertaining anymore. Therefore, the record carriers accordingto the present invention which are produced on basis of a masteringprocess can be accessed by corresponding record carrier reading devicesdue to the fact that the accumulated digital sum value lies below saidsecond predetermined limit and no such boosting occurs, but copiesthereof obtained by recording on a corresponding recordable recordcarrier cannot be properly accessed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiment given below, serve to explainthe principles of the invention, wherein:

FIG. 1 illustrates a CD frame comprising 588 channel bits,

FIG. 2 illustrates two cycles of one repetitive bit pattern according tothe present invention,

FIG. 3 illustrates an audio DC value corresponding to a first repetitivebit pattern with and without ramp signal according to the presentinvention,

FIG. 4 illustrates an audio DC value corresponding to a secondrepetitive bit pattern with and without ramp signal according to thepresent invention,

FIG. 5 illustrates a flow chart elucidating a first possibility toproduce an audio record carrier according to the present invention,

FIG. 6 illustrates a flow chart elucidating a second possibility toproduce an audio record carrier according to the present invention,

FIG. 7 illustrates a flow chart elucidating a possibility to produce adigital data record carrier according to the present invention,

FIG. 8 illustrates a flow chart elucidating a first possibility to copyan audio record carrier according to the present invention,

FIG. 9 illustrates a flow chart elucidating a second possibility to copyan audio record carrier according to the present invention,

FIG. 10 illustrates a flow chart elucidating a first possibility to copya digital data record carrier according to the present invention,

FIG. 11 illustrates a flow chart elucidating a second possibility tocopy a digital data record carrier according to the present invention,

FIG. 12 illustrates a data structure of an audio record carrier with andwithout the predetermined repetitive bit pattern according to thepresent invention, and

FIG. 13 illustrates a data structure of a digital data record carrierwith and without the predetermined repetitive bit pattern according tothe present invention.

The following description shows as an example how to modify the physicaldata stream of an audio CD to prevent copying the audio CD on a CD-R.The format of the physical data stream is specified in the ‘Red Book’specification and IEC 908.

The physical data stream on a CD is optimized in multiple ways to reduceerrors and guarantee a simple decoding mechanism. Therefore every 3 to11 bits must be a transition of the signal. Within the data symbols thisis guaranteed by the EFM (Eight-to-Fourteen Modulation). The audio datais split into 8 bit symbols which are converted to a 14 bit symbol withthe EFM table. This table consist of 256 entries of 14 bit values whichare combinations of bits which contain more than 2 but less than 10zeros continuously. Every ‘1’ in the 14 bit symbol represents atransition of the signal. To also guarantee this restriction whensymbols are concatenated there are additional 3 bits of merging, whichmust be chosen accordingly. On a CD these transitions can be seen inform of pits and lands. The length of each is bounded between 3 and 11times the base length.

The final frame of audio data, i.e. CD Raw sector, contains thefollowing data:   1 synchronization symbol  24 bits   1 subcode byte  14bits (EFM encoded)  24 data bytes 336 bits (EFM encoded)   8 paritybytes 112 bits (EFM encoded) 34*3 merging bits 102 bits TOTAL 588 bits

These bits, i.e. channel bits which fulfil the various constraints ofdigital recording as indicated above, are composed in the way as shownin FIG. 1. The order of one CD frame is as follows: the synchronizationpattern of 24 bits is followed by 3 auxiliary bits for merging and lowfrequency suppression; thereafter 14 bits subcode data are followed by 3auxiliary bits for merging and low frequency suppression; thereafter 12blocks of 14 bits information data are respectively followed by 3auxiliary bits for merging and low frequency suppression; thereafter 4blocks of 14 bits parity data are respectively followed by 3 auxiliarybits for merging and low frequency suppression; thereafter 12 blocks of14 bits information data are respectively followed by 3 auxiliary bitsfor merging and low frequency suppression; and finally 4 blocks of 14bits parity data are respectively followed by 3 auxiliary bits formerging and low frequency suppression.

As mentioned above, according to the present invention a repetitive bitpattern is inserted into the data stream (which can be audio samples ordigital data), or predetermined data, e.g. in case of audio such audiosamples corresponding to silence, is replaced by the predetermined bitpattern to ensure that the reading process of a copy of the masteredrecord carrier including said repetitive predetermined bit pattern willbe aborted or disturbed. As also mentioned above, this is achieved bysecuring that the predetermined repetitive bit pattern effects ageneration of a pit and land pattern on the record carrier which is notequally distributed, i.e. which shows either more pit parts than landparts or more land parts than pit parts. This is basically achieved bychoosing values for the replaced or inserted “audio or data samples”which result after the EFM in a predetermined bit pattern whichpreferably fulfils the requirement that only predetermined merging bitscan be inserted between the bits corresponding to the audio samples dueto the (2,10)-RLL requirement for normally ensuring no mismatch of pitparts and land parts, but according to the invention is used to ensurethe mismatch of pit parts and land parts.

In the following two example of such replaced or inserted “audio samplevalues” will be given in reference to FIGS. 2 to 4.

As inserted “audio sample” values which are inserted or which replace atleast one part of the digital data to be recorded, i.e. audio samples ofe.g. silence, in the first example, shown in FIG. 2 a, the hexadecimalvalues 70 and 01 are used. The combined value 7001h (h shows thehexadecimal notation) will be at least once repeated a predeterminedamount of times so that at least one part of the record carriercomprises the accumulated digital sum value that exceeds a firstpredetermined limit and that is below the second predetermined limit.

The value 70h corresponds to the bit pattern 01110000b (b shows thebinary notation) and the value 01h corresponds to the bit pattern00000001b. After the EFM the bit pattern 01110000b is converted into thebit pattern 10000000100010b and the bit pattern 00000001b is convertedinto the bit pattern 10000100000000b.

Due to the (2,10)-RLL requirement the three merging bits (the mergingbits are underlined in FIG. 2) between the EFM bit pattern10000000100010 and the EFM bit pattern 10000100000000 can only beselected to 000 and the three merging bits between the EFM bit pattern10000100000000 and the EFM bit pattern 10000000100010 can only beselected to 100.

The resulting channel bits for these two repetitive successivelyfollowing audio samples result in a bit stream as indicated in thebottom of FIG. 2 a which have a distribution corresponding to 22 bitslow (pit or land) and 12 bits high (land or pit), i.e. 22:12 instead ofthe ideal distribution of 17:17.

The audio DC value corresponding to the repetitive bit pattern 7001h iscomparatively low, i.e. a value 368 is achieved when the maximumachievable value is defined to 32768. This audio DC value is shown inFIG. 3, wherein FIG. 3 a shows the resulting audio DC value achievedwith insertion/replacement of predetermined audio samples by only thepredetermined repetitive bit pattern 7001h and FIG. 3 b shows theresulting audio DC value achieved with insertion/replacement ofpredetermined audio samples by the predetermined repetitive bit pattern7001h with preceding and succeeding ramp signal which assures a smooth(not hearable) transition from and to the audio DC values preceding andsucceeding the inserted/replaced part, in this case from and to an audioDC value zero.

As inserted “audio sample” values which are inserted or which replace atleast one part of the digital data to be recorded, i.e. audio samples ofe.g. silence, in the second example, shown in FIG. 2 b, the hexadecimalvalues D9 and 7A are used. As in the first example, the combined valueD97Ah will be at least once repeated a predetermined amount of times sothat at least one part of the record carrier comprises the accumulateddigital sum value that exceeds a first predetermined limit and that isbelow the second predetermined limit.

The value D9h corresponds to the bit pattern 11011001b and the value 7Ahcorresponds to the bit pattern 01111010b. After the EFM the bit pattern11011001b is converted into the bit pattern 10000000010001b and the bitpattern 01111010b is converted into the bit pattern 10010000000010b.

Due to the (2,10)-RLL requirement the three merging bits (the mergingbits are underlined in FIG. 2) between the EFM bit pattern10000000010001 and the EFM bit pattern 10010000000010 can only beselected to 000 and the three merging bits between the EFM bit pattern10010000000010 and the EFM bit pattern 10000000010001 can also only beselected to 000.

The resulting channel bits for these two repetitive successivelyfollowing audio samples result in a bit stream as indicated in thebottom of FIG. 2 b which have a distribution corresponding to 12 bitslow (pit or land) and 22 bits high (land or pit), i.e. 12:22 instead ofthe ideal distribution of 17:17.

The audio DC value corresponding to the repetitive bit pattern D97Ah iscomparatively high, i.e. a value 31449 is achieved when the maximumachievable value is defined to 32768. This audio DC value is shown inFIG. 4, wherein FIG. 4 a shows the resulting audio DC value achievedwith insertion/replacement of predetermined audio samples by only thepredetermined repetitive bit pattern D97Ah and FIG. 4 b shows theresulting audio DC value achieved with insertion/replacement ofpredetermined audio samples by the predetermined repetitive bit patternD97Ah with preceding and succeeding ramp signal which assures a smooth(not hearable) transition from and to the audio DC values preceding andsucceeding the inserted/replaced part, in this case from and to an audioDC value zero.

Of course, many other combinations of audio sample values or digitaldata sample values are possible which fulfil the general requirement ofencoding into channel bits having an the accumulated digital sum valuethat exceeds said first predetermined limit and is below said secondpredetermined limit.

FIG. 5 illustrates a flow chart elucidating a first possibility toproduce an audio record carrier according to the present invention. In afirst step S1 the source data and subcode to be recorded is read, e.g.from a data base storing the desired audio content and subcode data.Thereafter, in a second step S2 positions where the copy protectionpattern(s) according to the present invention should be inserted in thesource data, i.e. the audio data, are located, e.g. before and/or aftera music track and/or in a pause portion. Following the location of thepositions, the copy protection patterns are selected and generated in athird step S3 in which they are also inserted or added at the selectedpositions of the source data. In a next fourth step S4 the subcode getsmodified accordingly, e.g. start time information is adapted. Further,in a following fifth step S5 the modified source data (including thecopy protection patterns) and the modified subcode is sent to the signalfeeder of the mastering machine. Finally, in a sixth step S6 all stepsnecessary to produce a stamper are performed and in a seventh step S7discs are produced from the stamper.

FIG. 6 illustrates a flow chart elucidating a second possibility toproduce an audio record carrier according to the present invention. In afirst step S8 the source data and subcode to be recorded is read(similar to first the step S1 of the first possibility shown in FIG. 5).Thereafter, in a second step S9 positions where the copy protectionpattern(s) according to the present invention should be inserted in thesource data are located (similar to the second step S2 of the firstpossibility shown in FIG. 5). Following the location of the positions, amodification table for the signal feeder of the mastering machine isgenerated in a third step S10. The modification table includes thelocation of the copy protection patterns as well as these patternsitself. Further, also subcode modifications are included, if necessary.Finally, in a fourth step S11 all steps necessary to produce a stamperare performed and in a fifth step S12 discs are produced from thestamper (similar to the sixth step S6 and the seventh step S7 of thefirst possibility shown in FIG. 5).

FIG. 7 illustrates a flow chart elucidating a possibility to produce adigital data record carrier according to the present invention. In afirst step S14 the source data and subcode to be recorded is read, e.g.from a data base storing the desired digital data content (similar tofirst the step S1 of the first possibility shown in FIG. 5). Thereafter,in a second step S15 positions and/or files where the copy protectionpattern(s) according to the present invention should be inserted in thesource data are located. Following the location of the positions and/orfiles, the copy protection patterns are selected and generated in athird step S16 in which they are also inserted or added at the selectedpositions and/or the selected files of the source data. In a followingfourth step S17 the source data including the eventually modified filesare re-formatted. In a next fifth step S18 the subcode gets modifiedaccordingly, e.g. start time information is adapted. Further, in afollowing sixth step S19 the modified source data (including the copyprotection patterns) and the modified subcode is sent to the signalfeeder of the mastering machine. Finally, in a seventh step S20 allsteps necessary to produce a stamper are performed and in a eighth stepS21 discs are produced from the stamper (the fifth to eighth steps S18to S21 are similar to the fourth to seventh steps S4 to S7 of the firstpossibility to produce an optical audio record carrier shown in FIG. 5).

FIG. 8 illustrates a flow chart elucidating a first possibility to copyan audio record carrier according to the present invention. In a firststep S22 the source data and subcode to be copied is read, e.g. from anoriginal audio record carrier or a data base storing the content of anoriginal audio record carrier. Thereafter, in a second step S23 copyprotection pattern(s) according to the present invention are searched.Following the searching of the copy protection patterns, these patternsare replaced against other patterns or deleted in a third step S24. In anext fourth step S25 the subcode gets modified, if this is necessary,e.g. start time information is adapted. Further, in a following fifthstep S26 the modified source data and the eventually modified subcode issent to an optical recording system, e.g. of a PC. Finally, in a sixthstep S27 an optical disc is recorded by the optical recording system.

FIG. 9 illustrates a flow chart elucidating a second possibility to copyan audio record carrier according to the present invention. In a firststep S28 the source data and subcode to be copied is read, e.g. from anoriginal audio record carrier or a data base storing the content of anoriginal audio record carrier. Thereafter, in a second step S29 copyprotection pattern(s) according to the present invention are searched.Following the searching of the copy protection patterns, these patternsare replaced against other patterns or deleted in a third step S30. In anext fourth step S31 the subcode gets modified, if this is necessary,e.g. start time information is adapted (the first to fourth steps S28 toS31 are similar to the first to fourth steps S22 to S25 of the firstpossibility to copy an optical audio record carrier shown in FIG. 8).Further, in a following fifth step S32 the modified source data (notincluding the copy protection patterns) and the eventually modifiedsubcode is sent to the signal feeder of a mastering machine. Finally, ina sixth step S33 all steps necessary to produce a stamper are performedand in a seventh step S34 discs are produced from the stamper.

FIG. 10 illustrates a flow chart elucidating a first possibility to copya digital data record carrier according to the present invention. In afirst step S35 the source data and subcode to be copied is read, e.g.from an original digital data record carrier or a data base storing thedigital data content of an original data record carrier. Thereafter, ina second step S36 copy protection pattern(s) according to the presentinvention are searched. Following the searching of the copy protectionpatterns, these patterns are replaced against other patterns or deletedin a third step S37 (the first to third steps S35 to S37 are basicallysimilar to the first to third steps S22 to S24 of the first possibilityto copy an optical audio record carrier shown in FIG. 8). In a followingfourth step S38 the source data including the eventually altered filesare re-formatted, if this is necessary. In a next fifth step S39 thesubcode gets modified, if this is necessary, e.g. start time informationis adapted. Further, in a following sixth step S40 the modified sourcedata and the eventually modified subcode is sent to an optical recordingsystem, e.g. of a PC. Finally, in a seventh step S41 an optical disc isrecorded by the optical recording system (the fifth to seventh steps S39to S41 are basically similar to the fourth to sixth steps S25 to S27 ofthe first possibility to copy an optical audio record carrier shown inFIG. 8).

FIG. 11 illustrates a flow chart elucidating a second possibility tocopy a digital data record carrier according to the present invention.In a first step S42 the source data and subcode to be copied is read,e.g. from an original digital data record carrier or a data base storingthe content of an original digital data record carrier. Thereafter, in asecond step S43 copy protection pattern(s) according to the presentinvention are searched. Following the searching of the copy protectionpatterns, these patterns are replaced against other patterns or deletedin a third step S43 (the first to third steps S42 to S44 are basicallysimilar to the first to third steps S28 to S30 of the second possibilityto copy an optical audio record carrier shown in FIG. 9). In a followingfourth step S45 the source data including the eventually altered filesare re-formatted, if this is necessary. In a next fifth step S46 thesubcode gets modified, if this is necessary, e.g. start time informationis adapted. Further, in a following sixth step S47 the modified sourcedata (not including the copy protection patterns) and the eventuallymodified subcode is sent to the signal feeder of a mastering machine.Finally, in a seventh step S48 all steps necessary to produce a stamperare performed and in an eighth step S49 discs are produced from thestamper (the fifth to eighth steps S46 to S49 are basically similar tothe fourth to seventh steps S31 to S34 of the second possibility to copyan optical audio record carrier shown in FIG. 9).

To elucidate the difference for an unprotected record carrier and arecord carrier protected according to the present invention, the‘original layout’, i.e. the layout of an unprotected record carrier, andthe ‘changed layout’, i.e. one possibility of a layout of a recordcarrier protected according to the present invention, are shown in FIGS.12 and 13. FIG. 12 illustrates a data structure of an audio recordcarrier with and without the predetermined repetitive bit patternaccording to the present invention and FIG. 13 illustrates a datastructure of a digital data record carrier with and without thepredetermined repetitive bit pattern according to the present invention.The respective Fig. a shows the respective ‘original layout’ and therespective Fig. b shows the respective ‘changed layout’.

FIG. 12 a shows the original layout of an audio CD with a first lead-insection Lead-In 1, first to fourth audio tracks Audio Track 1 to 4, anda first lead-out section Lead-Out 1. Before the first three audio tracksAudio Track 1 to 3 a respective pause section of first to third pausesections P1 to P3 is arranged. FIG. 12 a shows the track number TrackNo. of each track, the index number Index of each section, the relativetime, i.e. the time of each track, and the absolute time, i.e. the totaltime of the disc.

The first lead in section Lead-In 1 has the track number 00 and no indexnumber. The following first pause section P1 before the first audiotrack Audio Track 1 has the track number 01 and the index number 00. Thefirst audio track Audio Track 1 has the track number 01 and the indexnumber 01. The following second pause section P2 before the second audiotrack Audio Track 2 has the track number 02 and the index number 00. Thesecond audio track Audio Track 2 has the track number 02 and the indexnumber 01. The following third pause section P3 before the third audiotrack Audio Track 3 has the track number 03 and the index number 00. Thethird audio track Audio Track 3 has the track number 03 and the indexnumber 01. The following fourth audio track Audio Track 4 has the tracknumber 04 and the index number 01. The following first lead-out sectionLead-Out 1 has the track number AA and the index number 01. The fouraudio tracks Audio Track 1 to 4, and the first lead-out section Lead-Out1 have a respective relative time R-Time which counts up from zero tothe real time corresponding to the respective section length. The threepause sections P1 to P3 have a respective relative time R-Time whichcounts down from the real time corresponding to the respective sectionlength to zero. The absolute time of the disc A-Time counts up from thebeginning of the first pause section P1 to the real time correspondingto the end of the first lead-out section Lead-Out 1.

FIG. 12 b shows the changed layout of an audio CD according to oneexemplary embodiment of the present invention which comprises first toseventh sections 1 to 7 comprising predetermined repetitive bitpattern(s) according to the present invention additionally to theoriginal layout shown in FIG. 12 a with a first lead-in section Lead-In1, four tracks Audio Track 1 to 4, three pause sections P1 to P3, and afirst lead-out section Lead-Out 1.

The first, fourth, and sixth sections 1, 4, and 6 are respectivelyarranged at (or directly after) the respective index change from 00 to01. A player will position it's reading optic at this respectiveposition in case a track is directly selected. The predeterminedrepetitive bit pattern(s) according to the present invention are veryefficient in such an area, since many players generally need a long timeto start playback or abort when such a direct positioning should beperformed on a recordable record carrier.

The second, fifth, and seventh sections 2, 5, and 7 are respectivelyarranged at the end of a track (section 2 at the end of the first trackAudio Track 1, section 5 at the end of the second track Audio Track 2,and section 7 at the end of the fourth track Audio Track 4). Theyenhance the efficiency of the copy protection scheme according to thepresent invention, in particular if they prolong the total duration ofthe predetermined repetitive bit pattern(s) according to the presentinvention, i.e. are arranged directly before or after another sectioncomprising the predetermined repetitive bit pattern(s) according to thepresent invention.

The third section 3 is arranged over the whole second pause section P2and therewith prolongs the total time of the predetermined repetitivebit pattern(s) according to the present invention by ‘connecting’ thesecond and the fourth sections 2 and 4. CD players show more problemswith long uninterrupted sections or uninterrupted connections ofsections comprising the predetermined repetitive bit pattern(s)according to the present invention than with short.

The sections comprising the predetermined repetitive bit pattern(s)according to the present invention are additionally inserted to theaudio data when being arranged before or after audio data and replacepause audio data, i.e. the first, second, and fourth to seventh sections1, 2, and 4 to 7 are additionally inserted and the third section 3replaces pause audio data.

In this example all pauses P1, P2, and P3 each have a length of 2seconds and all tracks Audio Track 1, Audio Track 2, Audio Track 3, andAudio Track 4 each have a length of 1 minute 30 seconds. The length ofthe first, second, fourth, fifth, sixth, and seventh sections 1, 2, 4,5, 6, and 7 each have a length of 1 second, the third section 3 has alength corresponding to that of the second pause P2. Therefore, thestart times of the tracks which are shown (besides other information) inthe table of contents TOC of the audio disc, have to be changed asfollows:

Original TOC Track Start Times of the Audio Disc

Track A-Time

-   01 00:02:00-   02 01:34:00-   03 03:06:00-   04 04:36:00-   AA 06:06:00    Modified TOC Track Start Times of the Audio Disc    Track A-Time-   01 00:02:00-   02 01:36:00-   03 03:10:00-   04 04:41:00-   AA 06:12:00

FIG. 13 a shows the original layout of a data disc with a second lead-insection Lead-In 2, a data track Data Track 1, and a second lead-outsection Lead-Out 2. Before the data track Data Track 1 a pregap sectionP is arranged and after the data track Data Track 1 a postgap section PGis arranged. FIG. 13 a shows the track number Track No. of each track,the index number Index of each section, the relative time, i.e. the timeof each track, and the absolute time, i.e. the total time of the disc.

The second lead in section Lead-In 2 has the track number 00 and noindex number. The following pregap section P before the data track DataTrack 1 has the track number 01 and the index number 00. The data trackData Track 1 has the track number 01 and the index number 01. Thefollowing postgap section PG has no individual track and index numbers.The following second lead-out section Lead-Out 2 has the track number AAand the index number 01. The data track Data Track 1 including thefollowing postgap section PG, and the second lead-out section Lead-Out 2have a respective relative time R-Time which counts up from zero to thereal time corresponding to the respective section length. The pregapsection P has a relative time R-Time which counts down from the realtime corresponding to the respective section length during access tozero. The absolute time of the disc A-Time counts up from the beginningof the pregap section P to the real time corresponding to the end of thesecond lead-out section Lead-Out 2.

FIG. 13 b shows the changed layout of a data CD according to oneexemplary embodiment of the present invention which comprises eighth toeleventh sections 8 to 11 comprising predetermined repetitive bitpattern(s) according to the present invention additionally to theoriginal layout shown in FIG. 13 a with a second lead-in section Lead-In2, a data track Data Track 1, a pregap section P, a postgap section PG,and a second lead-out section Lead-Out 2.

The eighth section 8 is arranged at (or directly after) the respectiveindex change from 00 to 01. A player will position it's reading optic atthis respective position when a disc is inserted into the player anddata is retrieved from the disc. As mentioned above, the predeterminedrepetitive bit pattern(s) according to the present invention are veryefficient in such an area, since many players, in this case CD-ROMreaders, generally need a long time to start playback or refuse to readthe disc when a recordable record carrier is used.

The ninth and tenth sections 9 and 10 are respectively arranged withinthe data track. The predetermined repetitive bit pattern(s) according tothe present invention might be inserted as ‘dummy data’ at the end offiles as an addition to the user data, or might be stored as ‘dummyfiles’ which do not store any user data, but only the predeterminedrepetitive bit pattern(s) according to the present invention.

The eleventh section 11 is arranged at the end of the data track. Itenhances the efficiency of the copy protection scheme according to thepresent invention.

The sections comprising the predetermined repetitive bit pattern(s)according to the present invention may replace existing data (e.g.00-data) or are additionally inserted to the original data (e.g. when‘dummy files’ are added within the data structure or ‘dummy data’ isarranged at the end of the data track.

In this example the pregap section P has a length of 2 seconds and thedata track Data Track 1 including the postgap section PG has a length of15 minutes 00 seconds. Therefore, in case the eighth section 8 replaces00-data and the ninth to eleventh sections 9 to 11 each have a length of1 second, the start times of the tracks which are shown (besides otherinformation) in the table of contents TOC of the data disc, have to bechanged as follows:

Original TOC Track Start Times of the Data Disc

Track A-Time

-   01 00:02:00-   AA 15:02:00    Modified TOC Track Start Times of the Data Disc    Track A-Time-   01 00:02:00-   AA 15:05:00

Of course, the track structure of the modified audio and data discsaccording to the present invention fulfil the requirements of theRed-Book, Yellow-Book or IEC-908, in which standards the different usedterms such as pause, pregap, postgap, track, index, A-Time, R-Time andTOC are further explained.

According to the present invention, as other copy protection methods,also both methods of confusing decoding as shown in the above referencedWO 01/78074, i.e. the confusion of the clock regeneration and confusionof synchronization and timing can be used for copy prevention togetherwith the copy protection scheme according to the present invention.Further, also the arrangement of a recursive session pointer as shown inthe above referenced WO 01/78074 might be used alone or in combinationwith said confusing decoding together with the copy protection schemeaccording to the present invention. However, in such a case theadvantage of the present invention that general purpose reading devices,like CD-ROM readers, can access the copy protected record carriers mightget lost.

Similar modifications as elucidated above for CDs can be done for DVD,which uses similar layout of the signal and for the decoding process.

1. Method to produce a copy protected record carrier for digital data,characterized by determining at least one predetermined repetitive bitpattern which encodes into channel bits having an accumulated digitalsum value that exceeds a first predetermined limit and that is below asecond predetermined limit, replacing at least one part of the digitaldata to be recorded by the at least one predetermined repetitive bitpattern and/or inserting the at least one predetermined repetitive bitpattern into at least one part of the digital data to be recorded, andtransferring said digital data including the at least one replacedand/or inserted part onto said record carrier by a mastering process sothat said accumulated digital sum value which exceeds said firstpredetermined limit and is below said second predetermined limit isachieved in said at least one replaced and/or inserted part.
 2. Methodaccording to claim 1, characterized in that said predeterminedrepetitive bit pattern is selected so that an abnormal writing beamdeviation from the ideal position of a writing beam of a record carrierrecording device for recordable record carriers which writing beamdeviation is big enough to ensure that a writing process will be abortedor disturbed.
 3. Method according to claim 1, characterized in that saidpredetermined repetitive bit pattern is selected so that an abnormalreading beam deviation from the ideal position of a reading beam of arecord carrier reading device which reads a copy of the copy protectedrecord carrier recorded on a recordable record carrier which readingbeam deviation is big enough to ensure that a reading process will beaborted or disturbed.
 4. Method according to claim 1, characterized inthat said predetermined repetitive bit pattern is selected so that anabnormal writing beam deviation from the ideal position of a writingbeam of a record carrier recording device for recordable record carriersand is selected so that a abnormal reading beam deviation from the idealposition of a reading beam of a record carrier reading device whichreads a copy of the copy protected record carrier recorded on arecordable record carrier wherein the combined effect of writing beamdeviation and reading beam deviation is big enough to ensure that areading process will be aborted or disturbed.
 5. Method according toclaim 1, characterized in that said predetermined repetitive bit patternis selected so that an abnormal reading beam deviation from the idealposition of the reading beam of a record carrier reading device whichreads the copy protected record carrier which deviation is small enoughto ensure a readability of the copy protected record carrier.
 6. Methodaccording to claim 1, characterized in that said predeterminedrepetitive bit pattern is selected so that merge bits are predefined andtherefore not changeable by the recording electronic of a recorder dueto design rules of the digital data content of the record carrier. 7.Method according to claim 1, characterized in that said predeterminedrepetitive bit pattern is selected so that the signal corresponding tothe digital data shows a certain positive or negative digital sum valuewithin a predefined time.
 8. Method according to claim 1, characterizedin that in case of audio, said predetermined repetitive bit pattern ispreferably selected so that a low analog audio DC value is achieved. 9.Method according to claim 1, characterized in that in case of audio,said predetermined repetitive bit pattern is preferably selected so thatan equal analog audio DC value in all audio channels is achieved. 10.Method according to claim 1, characterized in that in case of audio,said predetermined repetitive bit pattern is preferably selected so thatan audio output signal corresponding to the digital data is achieved,which analog audio output signal has a frequency and/or amplitude whichcannot be heard or can hardly be heard by humans.
 11. Method accordingto claim 1, characterized in that in case of audio, before and aftersaid predetermined repetitive bit pattern a ramp signal is added whichensures a smooth transition from and to the digital data signal contentbefore and after the signal content of the predetermined repetitive bitpattern.
 12. Computer program product, comprising computer program meansadapted to perform the method steps as defined in claim 1 or partsthereof when being executed on a computer, digital signal processor, orthe like.
 13. Device to produce a record carrier with copy protection,characterized by a first unit for replacing at least one part of thedigital data to be recorded by at least one predetermined repetitive bitpattern and/or for inserting at least one predetermined repetitive bitpattern into at least one part of the digital data to be recorded,wherein said repetitive bit pattern encodes into channel bits having anaccumulated digital sum value that exceeds a first predetermined limitand that is below a second predetermined limit, and a second unit fortransferring said digital data including the at least one replacedand/or inserted part to a record carrier production unit which producessaid record carrier by a mastering process so that said accumulateddigital sum value that exceeds a first predetermined limit and is belowa second predetermined limit is achieved in said at least one replacedand/or inserted part.
 14. Copy protected record carrier, characterizedby at least one part comprising at least one predetermined repetitivebit pattern which encodes into channel bits having an accumulateddigital sum value that exceeds a first predetermined limit and is belowa second predetermined limit.
 15. Method to copy digital data stored ona record carrier with copy protection onto a recordable record carrier,characterized by searching for at least one part of digital data to becopied onto said recordable record carrier comprising at least onepredetermined repetitive bit pattern which would encode into channelbits having an accumulated digital sum value that exceeds a firstpredetermined limit and is below a second predetermined limit, andreplacing said at least one part by a bit pattern which encodes intochannel bits having an accumulated digital sum value that is below saidfirst predetermined limit, or for deleting said at least one part. 16.Method to copy digital data stored on a record carrier with copyprotection onto a recordable record carrier, characterized by searchingfor at least one part of digital data to be copied onto said recordablerecord carrier comprising at least one predetermined repetitive bitpattern which would optimally encode into channel bits having anaccumulated digital sum value that exceeds a first predetermined limitand is below a second predetermined limit, and encoding said at leastone part non optimal into channel bits having an accumulated digital sumvalue that is below said first predetermined limit.
 17. Computer programproduct, comprising computer program means adapted to perform the methodsteps as defined in claim 15 when being executed on a computer, digitalsignal processor, or the like.
 18. Computer storage means, comprising acomputer program product according to claim
 17. 19. Device to copydigital data stored on a record carrier with copy protection onto arecordable record carrier, characterized by a searching unit to searchfor at least one part of digital data to be copied onto said recordablerecord carrier comprising at least one predetermined repetitive bitpattern which would encode into channel bits having an accumulateddigital sum value that exceeds a first predetermined limit and is belowa second predetermined limit, and a replacement unit for replacing saidat least one part by a bit pattern which encodes into channel bitshaving an accumulated digital sum value that is below said firstpredetermined limit, or for deleting said at least one part.
 20. Deviceto copy digital data stored on a record carrier with copy protectiononto a recordable record carrier, characterized by a searching unit tosearch for at least one part of digital data to be copied onto saidrecordable record carrier comprising at least one predeterminedrepetitive bit pattern which would optimally encode into channel bitshaving an accumulated digital sum value that exceeds a firstpredetermined limit and is below a second predetermined limit, and anencoding unit for encoding said at least one part non optimal intochannel bits having an accumulated digital sum value that is below saidfirst predetermined limit.
 21. Computer program product comprisingcomputer program means adapted to perform the method steps as defined inclaim 16 when being executed on a computer, digital signal processor, orthe like.
 22. Computer storage means, comprising a computer programproduct according to claim 21.